It is known that patient pain can be alleviated by the application of electrical pulses to stimulate nerves in the body. Nerves in the human body exhibit an all or none depolarization action to electrical stimulation; that is, if the electrical stimulus input is not of sufficient intensity to reach the depolarization threshold for the time it is applied to the nerve, no nerve depolarization will result. Strength-duration, S-D, curves for nerves are a plot of stimulus intensity versus pulse duration. The curves exhibit a common hyperbolic or inverse logarithmic shape over a wide range of pulse widths. The only difference in S-D curves from one class of nerves to another is the amplitude scale. The smaller nerve requires the largest depolarizing amplitude at a given pulse width.
Pain is a subjective phenomenon. The degree of pain relief is a subjective interpretation. By the study of the post treatment behavior of pain patients, one can assess treatment quality. It has been observed that a pain patient using a transcutaneous electrical nerve stimulation device provided with variable pulse width can get pain relief to a greater degree than a similar device having a fixed setting of pulse width. Patient portable instrumentation has been used for the treatment of chronic pain. These instruments stimulate the touch fiber nerves from the skin surface. The instruments have intensity controls, such as a single amplitude control. These instruments are further classified as to wave form: alternating square waves, spike exponential waves, symmetrical square waves, and square-spike combination waves. In the square wave units, means are provided for variation of intensity, the pulse widths, and the pulse repetition rate.